A valve timing control apparatus configured to change an opening and closing timing of an intake valve and an exhaust valve depending on an operation condition of an internal combustion engine (which will be hereinafter referred to as an engine) has been developed. Such valve timing control apparatus includes, for example, a configuration in which a relative rotation phase of a driven-side rotation member relative to a driving-side rotation member that rotates by an engine operation is changed so as to change the opening and closing timing of the intake valve and the exhaust valve opening and closing in association with the rotation of the driven-side rotation member.
An optimum opening and closing timing of the intake valve and the exhaust valve depends on the operating condition of the engine, for example, depends on whether the engine is started or the vehicle is being driven. At a time of the engine start, the relative rotation phase of the driven-side rotation member relative to the driving-side rotation member is locked at a predetermined phase so as to realize the optimum opening and closing timing of the intake valve and the exhaust valve. At this time, however, in a case where the relative rotation phase is maintained at the aforementioned predetermined rotation phase during an idling of the engine after the engine start, hydrocarbon emissions (HC emissions) may increase. Thus, during the idling of the engine after the engine start, the relative rotation phase is desired to be changed to a certain phase at which the HC emissions are restrained.
JP2011-1852A, which will be hereinafter referred to as Reference 1, discloses a valve timing control apparatus including an inner rotor arranged at an inside of a housing that is connected to a camshaft. The inner rotor serves as the driven-side rotation member while the housing serves as the driving-side rotation member. According to the valve timing control apparatus disclosed in Reference 1, fluid chambers are defined by the housing and the inner rotor. Then, each of the fluid chambers is divided by a vane serving as a partition member into an advanced angle chamber and a retarded angle chamber. In addition, an oil control valve (OCV) for relative rotation is provided to select one of the retarded angle chamber and the advanced angle chamber for supplying hydraulic oil serving as fluid to the selected chamber, thereby shifting the relative rotation phase between the housing and the inner rotor in either a retarded angle direction or an advanced angle direction. Further, a torsion spring is provided to extend from the inner rotor to the housing for biasing and displacing the relative rotation phase in the advanced angle direction.
According to the valve timing control apparatus disclosed in Reference 1, a first restriction member and a second restriction member are provided at the housing. In addition, a first restriction groove engaging with the first restriction member and a second restriction groove engaging with the second restriction member are formed at the inner rotor. The first restriction member and the second restriction member are insertable and retractable relative to the first restriction groove and the second restriction groove respectively. The first restriction member and the second restriction member project into the first restriction groove and the second restriction groove by means of a biasing force of the torsion spring. Further, a first connection passage for applying a pressure of hydraulic oil in a direction in which the first restriction member is retracted from the first restriction groove and a second connection passage for applying a pressure of hydraulic oil in a direction in which the second restriction member is retracted from the second restriction groove are formed at the inner rotor.
The first restriction member is fitted to the first restriction groove while the second restriction member is fitted to the second restriction groove to thereby obtain an intermediate lock phase. In addition, the second restriction member is retracted from the second restriction groove while the first restriction member makes contact with an end portion of the first restriction groove at a retarded angle side to thereby obtain a retarded angle restriction phase.
According to the aforementioned valve timing control apparatus disclosed in Reference 1, an oil control valve (OCV) for restriction portion is provided to supply the hydraulic oil separately and individually to the first restriction groove and the second restriction groove. As a result, the first restriction member and the second restriction member are retracted from the respective first restriction groove and the second restriction groove individually and separately, i.e., the retraction of the first restriction member from the first restriction groove is separately conducted from the retraction of the second restriction member from the second restriction groove. According to the OCV for restriction portion, the relative rotation phase is locked at the intermediate lock phase at which an improved startability of the engine is obtained when the engine is started. On the other hand, the relative rotation phase is restricted or locked at the retarded angle restriction phase positioned at the retarded angle side relative to the intermediate lock phase by the displacement of the relative rotation phase to the retarded angle side to thereby restrain the HC emissions during the idling of the engine after the engine start.
Generally, the inner rotor receives a displacing force in the advanced angle direction and a displacing force in the retarded angle direction based on a torque fluctuation of the camshaft. Specifically, the average displacing force is applied in the retarded angle direction so as to displace the inner rotor in the retarded angle direction. Hereinafter, the average of displacing forces in the retarded angle direction and the advanced angle direction based on the torque fluctuation of the camshaft will be described as an “average displacing force in the retarded angle direction based on the torque fluctuation of the camshaft”. According to the valve timing control apparatus, the relative rotation phase may be smoothly and promptly displaced in the advanced angle direction by the torsion spring regardless of the average displacing force in the retarded angle direction based on the torque fluctuation of the camshaft.
In view of environmental concerns, recent vehicles are equipped with an idling stop function for temporarily stopping the engine operation when stopping at a red light, for example, during the driving. In the idling stop state, the relative rotation phase is shifted to the most retarded angle phase to stop the engine because of the following reason. Because the engine is at a high temperature in the idling stop state, an ignition of air-fuel mixture for starting the engine may be easily performed when the engine is started with the relative rotation phase at the most retarded angle phase. In addition, in a case of cranking of the engine with the relative rotation phase at the most retarded angle phase, the rotation of the crankshaft may be smoothly started at a low load.
In a case where the engine is started while the engine is at a high temperature, however, a supply pressure of hydraulic oil is relatively low because of a high temperature and a low viscosity of hydraulic oil in addition to the low rotation speed of the engine. Thus, the supply pressure of hydraulic oil may not be sufficient for stably holding or maintaining the relative rotation phase.
During the operations of the inner rotor and the vanes at the time of the engine start in the idling stop state, according to the valve timing control apparatus disclosed in Reference 1, the displacing forces in the retarded angle direction and the advanced angle direction based on the torque fluctuation of the camshaft and the biasing force of the torsion spring are dominant over the supply pressure of hydraulic oil. That is, the average displacing force in the advanced angle direction based on the torque fluctuation of the camshaft is offset by the biasing force of the torsion spring in the advanced angle direction, which may inhibit the relative rotation phase from being stably maintained. Therefore, at the most retarded angle phase at which the housing and the inner rotor are inhibited from being mechanically locked or restricted, the inner rotor and the vanes move in the retarded angle direction and the advanced angle direction, which may cause each of the vanes to hit a wall surface of the fluid pressure chamber, thereby generating a hitting sound.
A need thus exists for a valve timing control apparatus which is not susceptible to the drawback mentioned above.